VWF Assays and Hemolysis

Here are two new questions from Kim Kinney at Clarian in Indianapolis:

We are validating VWF antigen and VWF activity (automated ristocetin cofactor) on our new TOP analyzer using the IL kits.  One issue we see is that the kits are not very forgiving when it comes to hemolysis. Now, I know, hemolyzed samples are not the best, but, we see a high number of kids from Riley Children’s Hospital that have had DDAVP challenges with severe hemolysis post dose.  It is almost a given that the post samples will be hemolyzed. Could it be the DDAVP or is it just the drawing from a catheter?

Also, we were establishing our reference ranges and the new ranges were quite a bit lower than the old.  So low that they did not correlate well with our old ristocetin cofactor and antigen assays.  Most of these samples were frozen Did I read somewhere that freezing can decrease your VWF levels?

Hi, Kim. It looks like your changeover to the TOP instrument is going well overall, though it generates a few challenges.

I did a quick literature review and came up with nothing that links DDAVP challenges with hemolysis, so I am sending this out to our participants for comment. i wonder whether the hemolysis is technique related.

I’m not surprised that the new method generates new reference ranges, given the high CVs generated in the CAP surveys for various labs reporting VWF:Ag and VWF:RCo. You will probably have to publish your new ranges and continue with the same methods.

In my personal experience, one freeze-thaw cycle will not affect plasma VWF results, though repeated freeze-thaw seems to break down the large multimers. My experience doesn’t include long-term storage, however, so the VWF level could be associated with aliquot age. Geo